Slice the flank steak against the grain into very thin strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, minced ginger, minced garlic, arrowroot powder, and water to create the stir-fry sauce.
Heat the sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the skillet in a single layer and sear for 2 minutes until browned, then remove the beef and set aside.
Add the broccoli florets to the same skillet with a splash of water, cover with a lid, and steam for 2-3 minutes until bright green and tender-crisp.
Return the beef to the skillet and pour the prepared sauce over the mixture.
Toss everything together for 1 minute until the sauce thickens into a glossy glaze that coats the beef and broccoli.
Garnish with sesame seeds and red pepper flakes before serving immediately.